Chronic infection with hepatitis B virus (HBV) is a major cause of chronic liver disease, cirrhosis and hepatocellular carcinoma (HCC) worldwide. Globally there are an estimated 400 million persons infected with HBV. In the United States, there are 1.25 million affected individuals and the epidemiology of the infection is changing with immigration of persons from endemic regions. The natural history of chronic hepatitis B (CHB) also appears to be changing with an increasing prevalence of HBeAg negative chronic hepatitis B. Knowledge of the rate of progression between individuals with HBeAg positive and negative CHB is unknown. An equally important and related issue is the clinical assessment of disease severity. Unfortunately, there are no good laboratory markers of disease severity. Liver biopsy is the accepted gold standard for assessing disease severity and cirrhosis but is costly, invasive, and associated with complications, which often limits patient acceptability as well as being subject to sampling error ranging from 15% to 25%. Non-invasive methods to assess disease severity are highly desirable for physicians caring for patients with CHB. Despite the recent licensing of several new agents for treatment of CHB, therapy remains problematic due to the high rate of anti-viral drug resistance with nucleos(t)ide analogues and relatively poor response to interferon. Identifying the optimal regimen and defining the best parameters to monitor patients both on and off therapy are major unresolved issues. Given the number of chronically infected persons and the requirement for long-term therapy in many of these patients, newer agents with different therapeutic targets are needed, as well as cheaper, more effective regimens. Hypotheses/problems addressed: 1) Define the host, viral and environmental factors that determine the natural history and outcome of HBV infection. To study this problem, we are creating a large database of untreated and treated patients with CHB (n400), which will be analyzed to identify factors that affect the natural history of chronic HBeAg positive and negative infections. This data will be used to develop a non-invasive model to predict fibrosis progression in patients with CHB. We also plan to evaluate the role of transient ultrasound elastography (Fibroscan) to assess fibrosis stage in persons with CHB. These results will be compared to liver biopsy, MRI elastography and plasma will be stored for future proteomic analysis. The goal is to develop a series of blood and imaging tests that will obviate the need for liver biopsy in most patients with CHB. 2) Develop and evaluate novel, safer and more effective therapies for chronic viral hepatitis. Current therapy of CHB remains less than optimal. Relapse is common if treatment is discontinued after one year in the absence of HBsAg loss. Consequently, nucleos(t)ides must often be administered long-term or indefinitely. However, long-term use is associated with the development of antiviral resistance with resulting loss of clinical benefit. Therefore an important challenge in HBV management is how to use these agents most effectively to achieve a long-term response while avoiding the issue of antiviral resistance. Lamivudine was the first oral nucleos(t)ide analogue to be approved for therapy of CHB. We initiated a long-term trial of lamivudine 100 mg daily in 1995 for both HBeAg positive and negative CHB in an effort to gain insight into the long-term benefit and safety of lamivudine. This study revealed significant histologic improvement at 8 years including reversion of advanced fibrosis to normal findings. In addition, at 8-10 years clearance of HBsAg was observed in 25% of patients (compared to a one year rate of 0% to 2%). One case of hepatocellular carcinoma was observed. This data is important for advising patients on long-term prognosis with lamivudine therapy. One strategy to prevent the development of antiviral resistance is to administer combination therapy using agents with different resistant profiles. We have conducted a randomized trial of lamivudine and adefovir versus adefovir monotherapy in patients with HBeAg positive and negative CHB with and without resistance to lamivudine to assess the benefits and safety of combination therapy for management of patients with untreated and resistant CHB. Forty-one patients were enrolled into this trial. The primary endpoint was a combined biochemical, virological and histological response that was maintained to 196 weeks. At 48 weeks the proportion of patients with a combined endpoint was higher in the combination arm compared to the monotherapy arm. suppression 64% versus 42%, p=NS. However, at 196 weeks a significantly greater proportion of patients on combination therapy achieved a combined response compared to monotherapy 58% versus 26%. At both 48 and 196 weeks, patients receiving combination therapy achieved a greater degree of HBV DNA suppression compared to those randomized to monotherapy. No evidence of antiviral resistance was observed in the combination arm whereas at 196 weeks 32% of patients treated with adefovir monotherapy had evidence of genotypic resistance. Neither the combination of lamivudine and adefovir nor adefovir monotherapy was associated with significant side effects. These results suggest that combination therapy with lamivudine and adefovir may be more appropriate for long-term use. However, whether combination therapy will be necessary with more potent agents with better resistance profiles will need to be evaluated in future trials. These promising results have led us to evaluate the combination of tenofovir and emtricitabine compared to tenofovir for patients with CHB. Tenofovir is a nucleotide analogue that is more effective than adefovir at suppressing HBV DNA and has an excellent resistance profile. This study will examine the long-term efficacy and safety of tenofovir and emtricitabine versus tenofovir alone in patients with HBeAg positive and negative CHB with the goals of maintaining long-term viral suppression ands preventing the emergence of viral resistance. To date 15 patients have been enrolled and started on therapy. Long-term results are pending. Elucidate the viral pathogenesis of HBV infection and mechanisms of anti-viral resistance The course of CHB following the development of anti-viral resistance is highly variable with some patients showing continued viral suppression, some with an accelerated course and others who lie in-between. We hypothesized that following initial viral breakthrough, compensatory mutations that do not alter sensitivity to lamivudine but instead affect viral replication may account for the different clinical presentations observed. Indeed, compensatory mutations, which restore viral fitness, were observed more frequently in patients who progressed to cirrhosis compared to those who did not. We also demonstrated that the pattern of mutations associated with lamivudine resistance appears to be genotype dependent. The rtM204V mutation occurred more frequently with HBV genotype A whereas the rtM204I mutation was observed in all genotype C patients. In-vitro analysis of viral replication using the most common primary and secondary lamivudine resistance mutations in genotype A and C constructs did not reveal a replicative advantage of either mutation in a particular HBV genotype. Thus, an increased replication advantage does not explain the observed association between HBV genotype and mutation pattern. These results have clinical implications and suggest that lamivudine therapy should be changed early in patients who develop resistance to prevent the accumulation of mutations which may accelerate progression of liver disease.